1. Field of the Invention
The present invention relates to a Code Division Multiple Access (CDMA) packet data system, and more particularly, to a method for dynamic allocation of channels in a CDMA packet data system.
2. Background of the Related Art
Generally, a CDMA transmitter transmits data by multiplying a PN (Pseudo Noise) code after spreading the spectrum of the transmit frequency, and a CDMA receiver demodulates the data to the original bandwidth by multiplying the same PN code as that in transmission.
FIG. 1 illustrates a block diagram of a related art CDMA packet data system. The system includes a base station 20 and a plurality of terminals 1–N.
The plurality of terminals 1–N are typically grouped in as many groups as there are channels used in one base station 20. Channels in the CDMA system are distinguished by unique PN codes. For example, if a system has six terminals 1–6 (i.e., N is 6) and three channels in one base station 20, this base station 20 classifies the six terminals 1–6 into three groups. Each group uses one channel.
Terminals using the same channel (terminals in the same group) each monitor the occupied state of the channel in order to prevent collisions with data transmitted by other terminals in the channel. Thus, if one terminal in a group detects that the other terminals in the same group (and thus using the same PN code as that used by itself) are not currently occupying the channel, it starts to transmit data through the channel. In determining whether or not the channel is occupied, an idle signal transmitted from the base station to the terminal is used.
In the related art system, the terminal has to transmit packet data through the corresponding, pre-allocated channel, and cannot use other channels. This method for static allocation of channels in the related art CDMA packet data system will now be described in more detail.
If the number of channels used in the base station 20 is three, and there are six terminals 1–6 for this base station 20, the base station 20 allocates a channel to each terminal 1–6. For example, channel A is allocated to terminal 1, terminal 2, and terminal 3, channel B is allocated to terminal 4, and channel C is allocated to terminal 5 and terminal 6.
Terminals in each channel can access the base station 20 independently of other channels. The CDMA system distinguishes channels using a PN seed. That is, terminal 1, terminal 2, and terminal 3 use the same PN seed, but the terminals in channel A and the terminal in channels B and C use different PN seeds.
With respect to channel A, as shown in FIG. 2, terminal 1 detects whether or not channel A is in the idle state in step ST1. If it is determined that channel A is idle, terminal 1 transmits packet data through channel A, as shown in step ST2.
If a packet of data to be transmitted by terminal 3 is generated after terminal 1 transmits one packet of data in this way, terminal 3 also detects whether or not channel A is in the idle state, according to step ST1. If channel A is idle, the packet of data of terminal 3 is transmitted through channel A, as shown in step ST2.
In this way, terminal 1, terminal 2, and terminal 3 each transmit data packets through channel A without collision with other data at different time intervals in a uniform order.
With respect to channel B and channel C, data is transmitted without collision with other data in the same way as described for channel A.
A method of detecting the occupied state of a channel in the related art system will now be described. Generally, packet data transmitted from a terminal consists of a preamble and data. The preamble is used by the base station in order to acquire the synchronization and phase of data transmitted from the terminal.
When terminal 1 transmits a packet of data to the base station 20 through channel A, the base station 20 transmits a power control signal through channel A to terminal 1. This enables terminal 1 and the base station 20 to maintain a constant power after acquiring synchronization and phase using the preamble of the packet data. Therefore, terminal 1 performs power control using this power control signal, and the other terminals (terminal 2 and terminal 3) not transmitting packet data do not transmit data because they recognize this power control signal as a channel occupancy signal.
Once the packet data has been received through channel A, the base station 20 does not perform power control anymore. Instead, it transmits an idle signal to the terminal side through channel A. Therefore, the terminals (terminal 1, terminal 2, and terminal 3) allocated to channel A detect that channel A is not occupied, and a terminal of that channel having packet data to be transmitted thus transmits data.
This method of channel allocation has various problems. For example, terminal 4 (allocated to channel B) and terminals 5 and 6 (allocated to channel C) cannot access channel A. In addition, the terminals allocated to channel A cannot access channel B or channel C. Thus, when channel A is busy and channel B is idle, the terminals allocated to channel A cannot use channel B.
Additionally, in this method for static allocation of channels in the related art CDMA packet data system, since channels are allocated in advance before the terminals transmit packet data and packet data is transmitted using only the allocated channel, the efficiency of the channel is decreased because the traffic of the channel is non-uniformly distributed.
Additionally, in some systems, when a prescribed period of time elapses after the occurrence of the traffic, the base station checks the traffic state for a period of time, and reallocates a predetermined number of terminals to the channel. However, this method has the disadvantage in that the non-uniformity of the traffic cannot be solved right away, and requires that the traffic state be checked.
The above references are incorporated by reference herein where appropriate for appropriate teachings of additional or alternative details, features and/or technical background.